Magneto-telephonic apparatus



(ModeL) 2 Sheets$heet 1.

F. H. BROWN.

MAGNETO TELEPHONIG APPARATUS.

Patented May 4, 1886.

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2- Sheets-Sheet 2.

(ModeL) F. H. BROWN.

MAGNETO TELEPHONIG APPARATUS.

' 110.341.370. Patented-May 4,1886.

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7 25 Attorneys UNITED STATES PATENT OFFICE.

FRED. ll. BROWN, OF FORT YVORTH, TEXAS.

MAGNETO-TELEPHONIC APPARATUS.

SPECIFICATION forming part of Letters Patent No. 341,370, dated May 4, 1886.

Application filed July 15, 1885.

To all whom it may concern:

Be it known that I, FRED. H. BROWN, a citizen of the United States, residing at Fort Worth, in the county of Tarrant and State of Texas, have invented a new and useful Improvement in Magneto-Telephonic Apparatus, of which the following is a specification, reference being had to the accompanying drawings.

My invention relates to an improvement in magneto-telephonic apparatus; and it consists in the improved apparatus for transmitting vocal and other sounds by disturbing the magnetic tensions of a permanent magnet by vibrating a diaphragm over its poles, and thereby causing electrical pulsations in the helices of wire wound around the poles of said magnet, which pulsations are reproduced in the helix or helices of another magnet similarly connected in circuit, which electrical pulsations disturb the magnetic tension in the receiving-magnet and cause the diaphragm of this magnet to be deflected in harmonious vibrations with the disturbing diaphragm, the number of convolutions of wire in the transmitting-instrument being greater than in the receiving-instrument.

My invention further consists in a magneto telephonic system in which the magneto trans mitting-telephone has a magnetic field of greater intensity than that of its companion receiving-telephone, the said magnetic field varying in intensity in approximately the same proportion as the resistance between the said instruments.

My invention further consists in the peculiar construction and combination of devices, that will be more fully set forth hereinafter, and

particularly pointed out in the claims.

In the accompanying drawings, Figure 1 is a diagram representing a pair of my improved telephones connected in circuit. Fig. 2 is an elevation, partlyin section, of the transmitter. Fig. 3 is a similar view of the receiving-instrument.

The object of my invention is to provide an apparatus capable of transmitting and reproducing articulate speech and other sounds without the use of a battery-current.

A represents the transmitting-telephone, in which B is an inclosing-case, which is comferred material, and is provided with a mouth- Serial No. 171,700. (Model.)

piece, 0. To the lower side of this case, on its inner side, is secured a permanent magnet, which is composed of the straight magnetized bar a, one end of which extends out through and beyond the side of the case and forms a handle for the instrument. S represents one pole of the bar, and N the opposite pole thereof. To the extremejNbndLof the bar a is attached the S end of a magnetized arm, I), which arm is arranged directly in the center of the inclosing-case. A similar magnetized arm, 12, is secured to the bar at one side of the inclosing-case and parallel to arm I), theS end of'arm I). being also attached to the bar a. The arms I) b, with that portion of the bar a between them, form a permanent U shaped magnet having terminals of the same polarity. Helices of insulated wire, D, are wound around the parallel arms of the magnet, the arms being wound either both in the same direction or in diverse directions. This construction of the magnet gives it greatintensity and energy.

construction to the transmitting-telephone,

with the exception that the helix or helices of the former have a smaller number of convolutions of wire than the helix or helices of the transmittinginstrument. As shown at Fin Figfglj only the arm of the magnet in the center of the inclosing-case is provided with a helix of wire, in order to render the difference in the number of convolutions in the transmitting and receiving instruments apparent at a glance.

The operation of my invention is as follows: \Vhen a person speaks into the mouthpiece of the transmittinginstrument, the diaphragm is caused to vibrate and induces currents of electricity in the helices, which are transmitted to the helix of the receiving-instrument and influence the receiving-magnet to cause the receiving diaphragm to vibrate in consonance with the transmitting diaphragm, and

thus convey to the ears of the listener the sounds or words delivered'into the transmit ting-instrument.

In order to utilize all the energy of the magnet, my diaphragm is connected magnetically to the weaker of the parallel similar poles, and its center vib ates over the other similar pole. The center of the diaphragm vibrates out of contact with the terminal arm of the magnet. The amplitude of vibration is much less,or almost nothing, at the edge of the diaphragm, but is in consonance with the center thereof, the difference being only one degree, which is compensated for by attaching the diaphragm at its edge directly in magnetic contact with the weaker of the similar poles of the magnet.

Although the deflection of the diaphragm is less at the edge than at the center,the electrical 2o disturbance is rendered equal at this point to the disturbance at the center, by reason of attaching the edge of the diaphragm directly to the weaker pole, thus intensifying the magnetic field in which the disturbance takes place.

2 5 Heretofore it has been the common practice to make the receiving and transmitting instruments of this class interchangeable-that is to say, both are equipped with helices having the same number of convolutious. My

0 invention differs from this, in that I provide my transmittingtelephone with a greater number of convolutious of wire than the re ceiving-instrument, thus increasing the intensity of the magnetic field, because more con- 5 volutions of wire are immersed therein. A

larger area of the magnetic field is also intercepted by the wires, and consequently a higher electro-motive force and a greater quantity of 1 current are by this means obtained,which lato ter expression is equivalent to a greater intensity of current, this intensity of current being increased proportionally to the resistance of the circuit.

From tests that Ihave made I have arrived at the following to give the best results: For a short-distance telephone, to be used through a circuit having a resistance of from five (5) to forty (40) oh ms, I first construct a receivinginstrument having just a sufficient number of convolutious in its helix or helices to increase and diminish the complete saturation of the magnet and produce a sufiiciently intense magnetic attraction and repulsion of its diaphragm to satisfactorily reproduce speech.

The instrument is then tested by trying it in circuit with'transmitters having successively less and less intensity of current until I reach a limit beyond which an additional diminution of the intensity of current in the transmitter no longer reproduces speech with maximum distinctness. I then determine whether the receiver has moreconvolutions than necessary. Ifit has, the superfl uous resistance in its helix or helices and its additional coercive force render it less sensitive to the rapidly-alternating cur rents of the transmitter. I therefore proceed to unwind convolutious from the receiver, and

if it reproduces speech more satisfactorily I continue to unwind until the maximum efficiency is obtained. If, on the other hand, the unwinding of the wire diminishes efficiency, I proceed to add more convolutious to the receiver until maximum efficiency is obtained.

Having finished the receiver, I construct the transmitter with constant reference thereto. The receiver already made operates with a given intensity of current. If its diaphragm were in like manner mechanically vibrated by the voice, it would produce a current of like intensity; but this intensity is not sufficient to traverse the resistance of the circuit, plus the resistance of the helix or helices of another receiver, and have strength enough left to vibrate its diaphragm, so 'as to reproduce speech with maximum distinctness. For this reason I give to the transmitter more convolutious than the receiver, and this must be experimentally determined with each instrument made. I connect the receivers in a circuit of, say, forty (40) ohms resistance, and starting with a receiver for a transmitter I add. convolutions to its helices until speech is reproduced with maximum distinctness.

In the abovementioned current of forty (40) ohms resistance I find that if the receiver has a length of wire corresponding to forty (i0) ohms of No. 36 copper, the transmitter will attain maximum results when it has a number of convolutious corresponding to one hundred and twenty-five (125) ohms of the same size wire. This varies in each instrument, because no two magnets can be made having the same magnetic moment or the same degree of saturation, or even exactly the same quality of steel. Indeed, the resistance even of the wire that forms the helices varies. If it is to be used over a circuit of ten thousand (10,000)

ohms, I find that the transmitter works better i if a little more wire is added to it, which is approximately one-half (i) an ohm of wire for every additional one hundred to five hundred (500) ohms resistance of circuit, the exact amount being determined by experimental test.

In the above-mentioned trial through a circuit of forty (40) ohms resistance I found that the proportionate number of convolutious were as one hundred and twenty-five to fifty, (50.) In other instruments made as nearly as possible in the'saine way, I found the proportions of two hundred and ninety to two hundred and ten, in others fifty to forty, &c. I first concluded that the difference was dependent upon the difference in resistance of the helices of the transmitter and receiver; but I find that if a helix has a specific resistance of one hundred ohms when no core is inserted in it, the resistance is greater when a permanent magnetis inserted. I also find that if the specific resistance of the wire in the helix of the receiver is fifty ohms, when placed over the highly-intensified arm of the permanent magnetthis resistance is greatlyincreased, and especially so when the instrument is in lIO operation. I must therefore state that I have not yet determined why the transmitter must have a greater number of convolutions than the receiver in order to produce the best results. I only know that such is the fact. It

does not depend on the less resistance of the receiver, as I have supposed, but upon the greater intensity of current of the transmitter. The resistance may be the same in the two instruments, and yet thetransmitterhave a much greater number of convolutious. This I have done by using a larger magnet for the transmitter and slightly larger wire.

Having thus described my invention I claim 1. The combinatiomwith a transmitting-instrument having a permanent magnet, helices wound around the magnet, and a diaphragm arranged in proximity to the poles of the magnet, of a receiving-instrument of similar construction, connected in circuit with the transmitting-instrument, the number of convolutions of wire in the transmitting-instrument being greater than in the receivinginstrument, substantially as described.

2. The permanent magnet having parallel terminal arms of the same polarity and the extended arm of opposite polarity, one of the said parallel arms being located between the other parallel arm and the neutral point of the magnet,in combination with the diaphragm secured to one of the parallel arms and free to vibrate over the other, and a helix on one or each of the parallel arms, substantially as described.

3. In a magneto-telephonic system, a mag neto transmitting-telephone having a magnetic field of greater intensity than that of its companion magneto receiving-telephone, the said field varying in intensity in approximately the same proportion as the resistance between 

